Switch-mode speed controller for use with brushless DC fans

For use with brushless DC fans, the Microchip TC649 switch-mode fan speed controller is now available from RS Components. The device offers temperature proportional speed control accomplished using pulse width modulation (PWM). A thermistor (or other voltage output temperature sensor) connected to the VIN input furnishes the required control voltage of 1.25V to 2.65V (typical) for 0% to 100% PWM duty cycle. The TC649 automatically suspends fan operation when measured temperature (VIN) is below a user programmed minimum setting (VAS). An integrated start-up timer ensures reliable motor start-up at turn-on, coming out of shutdown mode, auto-shutdown mode or following a transient fault, says the company.